Soils are classified according to structure or the arrangement of soil particles.
Structure is basecPon the chemical characteristics of the parent rock material, the amount of weathering, availability of organic material, and the size of soil particles. Structure is the most important of soil’s physical properties.
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Structure also depends on the shape of soil particles, or “peek” Peds may be spherical, blocky, plate-like, or prism-shaped.
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a. Loose or single-grain – a structureless soil in which the particles show little tendency to stick to each other at all; common in coarse-textured materials and dry environments; very permeable.
b. Crumblike – light, rounded aggregates with little empty space inside the peds; typical of surface soils in tropical regions and some mid-latitude agricultural areas.
c. Granular – dense, rounded aggregates with little empty space inside the peds; typical of surface soils in tropical regions and some mid-latitude agricultural areas.
d. Blocky – compact and tightly fitted together, with less pore spaces than any of the above; common in sub-soils in humid regions; sub-angular blocky peds have slightly rounded corners; angular blocky peds are sharp-edged because they are more tightly compressed.